Technical Abstract:
How is grass productivity above- and below-ground affected by grazing at different heights or by leaving different residuals after grazing? A recent study found no simple answer to this question. Meadow fescue and orchardgrass were grazed by Holstein heifers to remove 50 or 100% of above-ground forage when sward height reached either 12 or 24 inches in each of two years. Above-ground net primary productivity (ANPP) was measured using a rising plate meter and below-ground net primary productivity (BNPP) was estimated using in-growth root cores. ANPP and BNPP in 2010 were greater than that in 2009, due to higher rainfall. Orchardgrass was more productive than meadow fescue in both years. Grazing to remove 100% of above-ground forage generally increased ANPP, but increased the time interval between grazing events and reduced grass persistence, particularly in meadow fescue. Grazing at a 24-inch sward height increased ANPP in 2010 when precipitation was above-average. There was no relationship between grazing management and BNPP in orchardgrass either year or in meadow fescue in the drier year. BNPP of meadow fescue was increased by grazing at a 24-inch sward height in the wetter year. Grazing management effects on ANPP are more consistent across grass species and environment than the effects on BNPP.